Progress at brookhaven in the design of helium-cooled power transmission systems

Following an extensive study of cryogenic power transmission systems under development in this country and abroad it was concluded at Brookhaven that a flexible superconducting ac cable appeared to be the best choice for an economical high-capacity underground system with superior technical characteristics. A form of niobium-tin has been developed for this application with an intrinsic low-loss performance at 60 Hz. In addition, it has been determined that the ac characteristics of many commercial forms of Nb3Sn are degraded by additives, these effects are described. A flexible cable will require a lapped plastic insulation which must possess necessary properties both at room temperature and at the operating temperature, these are listed together with a summary of test results. Several designs for the cryogenic envelope to contain the cable are under development, the design options and trade-offs are discussed. Using performance data based on present knowledge of helium-cooled cables, systems were designed for an actual utility company transmission corridor 43 miles long rated at 4800 MVA. These designs are costed and compared to conventional transmission facilities.